Jul. 17, 2012

Contagious yawning is a peculiar phenomenon. That we can “catch” yawns is in itself fascinating, but that we can’t catch them from just anyone -- that we are immune to the yawns of perfect strangers but highly susceptible to those of family members or friends -- makes this behavior all the more intriguing.

Why yawning is contagious is unclear, but scientists suspect that it is linked to empathy, the ability to relate to another person’s emotions or feelings. This idea has gained support from studies in humans and other animals, including our closest primate relative, the chimpanzee. In a recent investigation of chimpanzees, males were discovered to be more susceptible to catching yawns than females, with the implication being that empathy-based responses in chimpanzees are driven by the male hierarchical structure of their societies.

In fact, as the researchers pointed out in the PLoS One paper, in chimp societies yawning likely is important specifically for rest-activity transitions, which are governed in part by the emotional and arousal states of males at the top of the hierarchy. Thus, the demonstration of empathy through yawning contagion by inferior males may serve to not only maintain or strengthen social bonds but also synchronize group behavior, essentially ensuring that everyone is on the same page, ready to either rest or move.

The researchers arrived at their conclusions after presenting videos of yawning chimpanzees or resting but not yawning chimpanzees to adults from the same social group. They then measured the adults’ yawning response, assessed responses in the context of relationship quality, and compared the responses of males and females. They found that while relationship quality was unrelated to yawning response (which contradicts previous reports but may have been due to the small study size), the sex of the yawning individual in the video had a significant effect on response. This was evident in the high proportion of males that yawned in response to videos of yawning males, compared with the low proportions of males that responded to videos of females and of females that responded to videos of individuals of either sex.

A study published earlier this year, in which dogs were found to “catch” yawns from their human caretakers, further suggests that yawning contagion is an empathy-based response that helps synchronize social behavior. Interestingly, in that study, an auditory stimulus -- the sound of a human yawn -- rather than a visual stimulus prompted yawning in dogs. And similar to the report in humans of an ingroup-outgroup bias (with family and friends representing the “ingroup” and strangers the “outgroup”), dogs had a tendency to yawn more when they heard familiar yawns than when they heard unfamiliar yawns.

Of course, not all yawns are of the contagious sort, and those that are must have originated from a first yawn, a yawn with a physiological basis. While the physiological mechanism of yawning, similar to its social significance, is not fully understood, research has indicated that yawning may help regulate the temperature of the brain, perhaps by compensating for increases in body temperature that accompany well-established yawn-inducing conditions, such as fatigue and sleep deprivation.

And finally, if you aren’t yawning yet, you might be a few moments—some researchers have suggested that even just reading or thinking about yawning can elicit yawns in humans.

About Kara Rogers

Kara is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is the author of Out of Nature: Why Drugs From Plants Matter to the Future of Humanity (University of Arizona Press, 2012).

The views expressed are those of the author and are not necessarily those of Science Friday.